Drylands cover 41 percent of the Earth’s land surface. Of that area, desertification has rendered 20 percent unfit for human use, and an additional 70 percent remains vulnerable. According to the United Nations, desertification is degrading soil quality in 110 countries, directly impacting 250 million people and threatening a billion more, all without creating a single new desert.

“True deserts have evolved for millions of years,” says Exequiel Ezcurra, research director for the San Diego Natural History Museum. “When you get degradation in Oklahoma, you don’t get a desert popping up, you just get barren soil.”

The UN has declared 2006 the International Year of Deserts and Desertification. The latter phenomenon occurs around deserts on semi-arid and semi-tropical land, which is often used for grazing or cropland. “Desertification is caused by human activity and exasperated by climate impact,” explains David Mouat of the Desert Research Institute. Overgrazing and improper farm management leaves land vulnerable to being stripped bare, the result of erosion. Wind scatters the exposed soil during droughts, and water washes it away during rainfall.

According to Charles Hutchinson, director of Arid Land Studies at the University of Arizona in Tucson, desertification changes more than just the appearance of the landscape. “Once you’ve removed the cover of vegetation you’re going to change what’s going on in the soil. Many times it won’t recover. In many parts of Africa they’re getting “shrubification,” a change from grasslands to scrubland,” Hutchinson explains.

Though desertification endangers semi-arid lands in both Africa and Arizona, as well as in China and Spain, developing countries feel the consequences of denuded land more immediately. “What people do to cause desertification occurs in both developed and developing countries,” says Mouat. “The difference is in how people are affected and what they can do about it.”

Reversing the damage is impossible or too costly for developing nations, and the changes affect the livelihoods of local communities. “When biodiversity is impacted,” Mouat cautions, “that impacts people’s ability to extract goods and services from the land.” Herds no longer have the grasslands as a food source, and degraded soil does not produce crops. Desertification currently costs the world $42 billion worth of agricultural production a year.

A country’s desertification quickly becomes a problem for its neighbors as well. Dust clouds, drawn into the air by high-pressure systems over central China, have closed Korean airports, and Hutchinson claims that the same dust clouds make their way across the Pacific to North America. “When that surface is exposed it can be moved by wind,” he says, “and we’re tracking the movement of those plumes of dust over to the U.S.” The dust can cause eye infections and respiratory problems, though Mouat doubts that those effects will be particularly severe in the U.S. Still, he emphasizes the importance of an international response. “It’s important to recognize it’s a global problem,” he says, “not just because of the climate feedback, but because we’re a global society.”

Avigad Vonshak, director of Israel’s Jacob Blaustein Institutes for Desert Research (see Currents, this issue), agrees with Mouat’s conclusion, and takes it a bit further. “It’s a mistake to refer to desertification as something not affecting all of us,” he says. He cites dust storms as a factor in the 50 percent increase in eye infections over the past few years in U.S. and European babies. “Sand dunes in Africa are usually stabilized by a crust cover,” Vonshak says. “If you have humans acting in an unsustainable way, the natural cover is destroyed and the dunes can move and produce dust storms. This is globalization.”